The present invention relates to write once type optical recording and optical recording/reproducing methods using a laser beam, and an optical recording material and an optical recording device using the methods. More particularly, the present invention relates to optical recording and optical recording/ reproducing methods useful for a high recording density, and an optical recording material and an optical recording device using the methods.
There are enhanced needs for file memories of high density and capacity in accordance with higher development of the information society. An optical recording is noted as the memories for satisfying the needs. This optical recording is divided into read only type, write once type and erasable type, which are properly used for individual applications. Here, the write once type optical disc uses a chalcogenide as its recording material and is formed with pores when irradiated with a laser beam. The recording is carried by making use of a change in reflectivity due the pores.
The present investigation of the write once type optical disc is centralized for improving the recording density. For this improvement, it is conceived to form minute recording pits by using a laser beam having a short wavelength and to use a pit edge recording together. It is, however, difficult to form pits having a satisfactory shape from the existing materials.
An improved optical recording medium is disclosed in U.S. Pat. Nos. 4,176,277 and 4,405,862. This optical recording medium has a structure, in which a thermal sensitive film and an absorption film are laminated. The absorption film absorbs the recording beam and changes it into heat, which is diffused in the thermal sensitive film for the recording operation.
The prior art thus exemplified has a limit in forming recording pits of about 1 .mu.m, thus leaving a problem that the improvement in the recording density is limited.